1. Field of the Invention
The present invention relates to an exposure apparatus and a method for manufacturing the same, which has an excimer laser light source, a higher harmonics laser light source, a mercury lamp light source or the like, each radiating light having an ultraviolet range of a wavelength of, for example, 300 nm or shorter. The present invention also relates to an optical device for a projection optical system or an illumination optical system for use with such an exposure apparatus, and to a method for cleaning such an optical device.
2. Description of the Related Art
An exposure apparatus for exposing an image of a pattern of a reticle (a photomask or the like) onto a photosensitive substrate through a projection optical system has been employed in a lithography process for manufacturing semiconductor elements, liquid crystal substrates, and so on. Recent years, developments have been performed to make semiconductor integrated circuits finer and finer, and in order to comply with such finer integration of semiconductor circuits, there has been attempted to make shorter an exposing wavelength of a light source for use in a lithography process.
At a current time, an exposure apparatus has already been developed which uses a KrF excimer laser having a wavelength of 248 nm as a light source for a stepper. For example, a higher harmonic wave of a wavelength variable laser such as Ti-sapphire laser, etc., a quadruple harmonic wave of a YAG laser having a wavelength of 266 nm, a fivefold harmonic wave of a YAG laser having a wavelength of 213 nm, a mercury lamp having a wavelength close to 220 nm or a wavelength of 184 nm, and an ArF excimer laser having a wavelength of 193 nm draw attention as a candidate for a light source having a shorter wavelength.
For conventional exposure apparatuses which use g-rays, i-rays, a KrF excimer laser, or a mercury lamp emitting light rays having a wavelength close to 250 nm as a light source, emission spectral rays of such a light source do not overlap with an absorption spectral region of oxygen, so that they do not cause any decrease in efficiency of light utilization due to absorption of oxygen and do not suffer from any disadvantage resulting from the generation of ozone due to the absorption of oxygen. Therefore, those exposure apparatuses can basically be used for exposure in ambient atmosphere.
On the other hand, however, for a light source such as an ArF excimer laser, emission spectral rays overlap with an absorption spectral region of oxygen, so that a decrease in efficiency of light utilization may be caused by the adsorption of oxygen, and the disadvantage may also result from the generation of ozone due to the absorption of oxygen. For instance, if it is supposed that a transmittance of an ArF excimer laser light in vacuum or through an inert gas such as nitrogen or helium is 100%/m, the transmittance is decreased to approximately 90%/m, on the one hand, when the light is in a free-run state, i.e., in a natural emission state, that is, the light source is an ArF broad-banded laser, and it is decreased to approximately 98%/m, on the other hand, even when there is used an ArF laser with the spectral width narrowed and so narrow-banded as to avoid rays of absorption of oxygen.
It is considered that the decrease in transmittance is caused due to the absorption of light by oxygen and an influence of ozone generated. The generation of ozone is considered to exert an adverse influence upon the transmittance of light (i.e., efficiency of light utilization) as well as to cause a deterioration in performance of devices due to a reaction with a surface of an optical material or other parts and to cause a pollution of environment.
For the above-mentioned conventional exposure apparatuses having a light source such as an ArF excimer laser in the configuration as described above, it is well known that the entire area of a light passage is required to be filled with an inert gas such as nitrogen or the like, in order to avoid a decrease in transmittance of light and a generation of ozone.
As a result of various exposure experiments using a projection exposure apparatus with an excimer laser light source installed therein and having a relatively large field size, a new phenomenon has now been discovered in that the irradiation of an illuminating light in an ultraviolet region having a wavelength range of, for example 350 nm or less (e.g., KrF excimer laser having a wavelength of 248 nm or ArF excimer laser having a wavelength of 193 nm, etc.) dynamically fluctuates transmittance or reflectance of an optical element in a projection optical system or a coating material (e.g., a thin film for a reflection preventive film, or the like) for the optical element in the projection optical system. It is further found that this new phenomenon fluctuating the transmittance of light dynamically can be caused to occur in substantially the same way as not only in the case of an optical element disposed in the projection optical system but also in the case of an optical element disposed in an illumination optical system for illuminating a reticle. Moreover, likewise, it is also found that the such phenomenon is caused to occur in the case of an optical element in a light sending system leading the illuminating light leaving from a light source disposed under a floor of a clean room to an illumination optical system installed in the main body of the exposure apparatus, and in the case of the reticle (a quartz plate) itself.
In addition, the such phenomenon is considered to occur, for instance, due to the attachment of impurities contained in a gas (e.g., air, nitrogen gas, etc.) present in a space of a projection light passage or an illumination light passage, molecules of organic substances departing from adhesive or a filling material, etc., for use in fixing optical elements to a barrel, impurities (e.g., water molecules, hydrocarbon molecules, or other substances diffusing the illuminating light) derived from the inner wall) derived from an inner wall of the barrel (e.g., a coated surface for reflective prevention, etc.), or otherwise, or due to the entry (floating) of such impurities or otherwise into the illumination light passage. As a consequence, a serious problem is considered to be caused such that the transmittance or reflectance of the projection optical system, the illumination optical system, and the light sending system fluctuates to a great extent for a relatively short period of time.
The object of the present invention is to provide an optical device which is so arranged as for an optical element including, for example, lenses constituting a projection optical system, an illumination optical system or a light sending system, or a reflecting mirror or otherwise unlikely to be contaminated, to provide a method for cleaning the optical device, to provide an exposure apparatus using such a projection optical system, an illumination optical system or a light sending system, each being unlikely to be contaminated, which has been cleaned by the method for cleaning, and to provide a method for manufacturing the such exposure apparatus.
Further, the present invention has another object to provide an exposure apparatus that can prevent an optical characteristic (for example, transmittance or reflectance) of an optical member from fluctuating by irradiating the optical member with a radiating beam having a wavelength of, for example, 350 nm or less.
Moreover, the present invention has a further object to provide an exposure apparatus in which an optical member including, for example, an illumination optical system, a projection optical system or a light sending system or otherwise, each being incorporated in the exposure apparatus, is so arranged as to be cleaned.
In order to achieve the object as described above, the optical apparatus according to the present invention is configured in such a manner that a protective filter is disposed apart in a predetermined distance between the optical elements, among plural optical elements disposed in a barrel, which are disposed on the both end sides in the axial direction of the barrel, wherein chambers disposed between the plural optical elements and a space between the optical elements on each of the both end sides and the protective filter is filled with an inert gas in advance.
The optical device according to the present invention is installed in an apparatus for irradiating a mask with an illuminating light and exposing a substrate with the illuminating light through the mask, wherein an inert gas having the lower capability of absorbing the illuminating light is used as the inert gas to be filled therein. The illuminating light to be used therefor has a wavelength of 350 nm or less. Further, upon mounting the optical device on a light passage housing of the illumination optical system installed in the exposure apparatus, it is preferred that the protective filter is detached while the space is being purged with the gas and then the housing is filled with the inert gas, or that the protective filter is detached while the space is being purged with the gas and a fresh protective filter cleaned in advance is mounted on the both sides in an axial direction of the barrel, followed by filling the light passage with the inert gas.
In order to achieve the object as described above, the present invention according to another embodiment provides the optical device comprising a gas supply passage for supplying an inert gas to a barrel with a plurality of optical elements disposed therein; an supply inlet connected to the gas supply passage; a gas discharge outlet for discharging the inert gas present in the barrel; and a removing member for removing a contaminating material, disposed on an inner wall of the gas supply passage.
The optical device according to the another embodiment of the present invention is installed in a device for irradiating a mask with an illuminating light and exposing a substrate with the illuminating light through the mask, wherein a gas having a lower capability of absorbing the illuminating light is used as the inert gas. As the removing member, there may be used an adsorbing material or a filter.
In order to achieve the object as described above, the present invention according to a further embodiment provides an optical device for use with an exposure apparatus for transferring a pattern on a mask onto a substrate, in which the removing member for removing a contaminating material is mounted on an inner surface of a barrel with a plurality of optical elements disposed therein.
Further, in order to achieve the object as described above, the present invention provides the optical device according to a still further embodiment so adapted as to be used for an exposure apparatus that transfers a pattern on a mask onto a substrate by irradiating the mask with an illuminating light, wherein each of plural chambers formed between the plurality of the optical elements disposed in the barrel is provided with a gas supply inlet and a gas discharge outlet, respectively, for supplying and discharging an inert gas having a less capability of absorbing the illuminating light, and each of the gas supply inlet and the gas discharge outlet is provided with an opening-closing valve for opening and closing the gas supply inlet and the gas discharge outlet, respectively.
In addition, in order to achieve the object as described above, the present invention in another aspect provides a light cleaning method for cleaning the optical device for use with an exposure apparatus for transferring a pattern on a mask onto a substrate by irradiating the mask with an illuminating light, the optical device being configured in such a way that each of chambers formed between a plurality of optical elements disposed in a barrel is provided with a gas supply inlet and a gas discharge outlet for supplying and discharging a gas having a lesser capability of absorbing the illuminating light, respectively, and that the gas supply inlet and the gas discharge outlet are each provided with an opening-closing valve for opening and closing the gas supply inlet and the gas discharge outlet, respectively; wherein the optical device is cleaned by the light cleaning method comprising the step for filling the barrel with the gas to a predetermined pressure in such a state that the opening-closing valve of the gas supply inlet is opened while the opening-closing valve of the gas discharge outlet is closed; the step for allowing a contaminating material attached on a surface of the optical elements to float by irradiating the optical elements with the illuminating light in such a state that the opening-closing valves of the gas supply inlet and the gas discharge outlet are both closed; the step for flowing the gas outside and inside the barrel by opening the opening-closing valve of the gas supply inlet and the opening-closing valve of the gas discharge outlet; and the step for closing the opening-closing valves of the gas supply inlet and the gas discharge outlet, respectively.
With the above configuration, it is also possible to flow the inert gas through each of the plural chambers in such a state that the opening-closing valves of the gas supply inlet and the gas discharge outlet are both opened, prior to closing the opening-closing valve of the gas discharge outlet. Moreover, the optical device may be configured in such a manner that the plural chambers are divided into at least two groups, each group having a predetermined number of chambers, and each group is provided with a gas supply inlet and a gas discharge outlet as well as the gas supply inlet and the gas discharge outlet are each provided with an opening-closing valve.
Furthermore, in order to achieve the object as described above, the present invention provides a projection exposure apparatus for transferring a pattern on a mask onto a substrate through a projection optical system by irradiating the mask with an illuminating light, wherein a plurality of chambers, each chamber being formed between a plurality of optical elements disposed in a barrel and provided with a gas supply inlet and a gas discharge outlet for supplying and discharging an inert gas having a lesser capability of absorbing the illuminating light, respectively, and the gas supply inlet and the gas discharge outlet being each provided with an opening-closing valve; wherein the optical device is so arranged as to be cleaned by a light cleaning method comprising the step for filling the barrel with the gas to a predetermined level of pressure in such a state that the opening-closing valve of the gas supply inlet is opened while the opening-closing valve of the gas discharge outlet is closed; the step for allowing a contaminating material attached on a surface of the optical elements to float by irradiating the optical elements with the illuminating light in such a state that the opening-closing valves of the gas supply inlet and the gas discharge outlet are both closed; the step for flowing the gas outside and inside the barrel by opening the opening-closing valve of the gas supply inlet and the opening-closing valve of the gas discharge outlet; and the step for closing the opening-closing valves of the gas supply inlet and the gas discharge outlet, respectively.
The optical device according to the present invention may also be used as the projection optical system and/or the illumination optical system for irradiating the mask with the illuminating light.
In order to achieve the object as described above, the present invention in a further aspect provides an exposure apparatus for transferring a pattern on a mask onto a substrate, which comprises an optical system interposed between a light source for emitting an illuminating beam and the substrate; a protective filter disposed at least at an end of a barrel for holding an optical element; and an optical unit having a gas having a lesser capability of absorbing the illuminating beam filled in the barrel, the optical unit being disposed in the optical system.
With the above configuration, the optical device according to the present invention contains an illumination optical system for irradiating the mask with the illuminating beam and has the optical unit disposed in the illumination optical system. Upon mounting the optical unit on the optical system, the protective filter may be detached from the barrel or a new protective filter is exchanged for the older one. Preferably, the optical device according to the present invention is further provided with a gas supply device for supplying an inert gas having a lesser capability of absorbing the illuminating beam, which is disposed in the optical system, and the gas supply device is to be operated after the illuminating beam has been emitted in such a state that the optical system is filled with the inert gas. Moreover, it is preferred that the optical device is further provided with a gas exhaust device for discharging the inert gas present in the optical system and that the gas exhaust device is operated prior to filling or supplying the optical system with the inert gas. The illuminating beam to be used therefor may have a wavelength preferably in the range of from 100 nm to 200 nm, and it may preferably include, for example, ArF laser or F2 laser. Moreover, the inert gas may preferably include, for example, nitrogen, helium, or the like.
In addition, in order to achieve the object as described above, the present invention in a still further embodiment provides the exposure apparatus for transferring a pattern on a mask onto a substrate, which comprises an optical system interposed between a light source for emitting an illuminating beam and the substrate; a gas supply device for supplying an inert gas having a lesser capability of absorbing the illuminating beam to at least a portion of the optical system; and a gas exhaust device for discharging the inert gas from the portion of the optical system prior to the supply of the inert gas.
With the above configuration, the optical device according to the present invention may contain an illumination optical system for irradiating the mask with the illuminating beam, a light sending system interposed between the light source and the illumination optical system, and a projection optical system for projecting the illuminating beam leaving from the mask onto the substrate. With this configuration, it is preferred that the gas exhaust device and the gas supply device are operated one after another in this order after the optical system has been cleaned by means of light by irradiating the optical system with the illuminating beam. The illuminating beam to be used therefor may have a wavelength preferably in the range of from 100 nm to 200 nm, and it may preferably include, for example, ArF laser or F2 laser. Moreover, the inert gas may preferably include, for example, nitrogen, helium, or the like.
In order to achieve the object as described above, the present invention in a still further aspect provides a method for the production of the exposure apparatus, which comprises locating a protective filter at least at an end of a barrel holding optical elements, filling the barrel with an inert gas having a lesser capability of absorbing the illuminating beam, and locating the barrel between a light source for emitting the illuminating light and the substrate.
In the method for the production of the exposure apparatus according to the present invention, the protective filter is detached or a new protective filter is exchanged for the older protective filter, after the barrel has been disposed.
Moreover, in order to achieve the object as described above, the present invention in a still further embodiment provides a method for the production of the exposure apparatus for exposing the substrate to the illuminating beam through the mask, which comprises irradiating at least a portion of the optical system capable of allowing the illuminating beam to pass therethrough with a cleaning light for cleaning the optical system and replacing the gas present in the optical system with a gas having a lesser capability of absorbing the illuminating beam.